From patchwork Tue Jul 19 18:47:51 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 9238283 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 8CD70600CB for ; Tue, 19 Jul 2016 20:27:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7AFF626D19 for ; Tue, 19 Jul 2016 20:27:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6C5172756B; Tue, 19 Jul 2016 20:27:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 01D2826D19 for ; Tue, 19 Jul 2016 20:27:53 +0000 (UTC) Received: from localhost ([::1]:58603 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bPbcO-0000bN-1T for patchwork-qemu-devel@patchwork.kernel.org; Tue, 19 Jul 2016 16:27:52 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45644) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bPa45-0002D2-Ew for qemu-devel@nongnu.org; Tue, 19 Jul 2016 14:48:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bPa44-0005SB-D5 for qemu-devel@nongnu.org; Tue, 19 Jul 2016 14:48:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42617) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bPa44-0005Rz-4K for qemu-devel@nongnu.org; Tue, 19 Jul 2016 14:48:20 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A5CAE7F41A; Tue, 19 Jul 2016 18:48:19 +0000 (UTC) Received: from localhost (ovpn-112-17.ams2.redhat.com [10.36.112.17]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u6JImIuP026378; Tue, 19 Jul 2016 14:48:19 -0400 From: Stefan Hajnoczi To: Date: Tue, 19 Jul 2016 19:47:51 +0100 Message-Id: <1468954095-5159-2-git-send-email-stefanha@redhat.com> In-Reply-To: <1468954095-5159-1-git-send-email-stefanha@redhat.com> References: <1468954095-5159-1-git-send-email-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 19 Jul 2016 18:48:19 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL for-2.7 01/25] block: Fragment reads to max transfer length X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Stefan Hajnoczi Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Eric Blake Drivers should be able to rely on the block layer honoring the max transfer length, rather than needing to return -EINVAL (iscsi) or manually fragment things (nbd). This patch adds the fragmentation in the block layer, after requests have been aligned (fragmenting before alignment would lead to multiple unaligned requests, rather than just the head and tail). The return value was previously nebulous on success on whether it was zero or the length read; and fragmenting may introduce yet other non-zero values if we use the last length read. But as at least some callers are sloppy and expect only zero on success, it is easiest to just guarantee 0. [Fix uninitialized ret local variable in bdrv_aligned_preadv(). --Stefan] Signed-off-by: Eric Blake Message-id: 1468607524-19021-2-git-send-email-eblake@redhat.com Signed-off-by: Stefan Hajnoczi --- block/io.c | 57 +++++++++++++++++++++++++++++++++++---------------------- 1 file changed, 35 insertions(+), 22 deletions(-) diff --git a/block/io.c b/block/io.c index cfda714..c3574a4 100644 --- a/block/io.c +++ b/block/io.c @@ -971,21 +971,25 @@ err: /* * Forwards an already correctly aligned request to the BlockDriver. This - * handles copy on read and zeroing after EOF; any other features must be - * implemented by the caller. + * handles copy on read, zeroing after EOF, and fragmentation of large + * reads; any other features must be implemented by the caller. */ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs, BdrvTrackedRequest *req, int64_t offset, unsigned int bytes, int64_t align, QEMUIOVector *qiov, int flags) { int64_t total_bytes, max_bytes; - int ret; + int ret = 0; + uint64_t bytes_remaining = bytes; + int max_transfer; assert(is_power_of_2(align)); assert((offset & (align - 1)) == 0); assert((bytes & (align - 1)) == 0); assert(!qiov || bytes == qiov->size); assert((bs->open_flags & BDRV_O_NO_IO) == 0); + max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX), + align); /* TODO: We would need a per-BDS .supported_read_flags and * potential fallback support, if we ever implement any read flags @@ -1024,7 +1028,7 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs, } } - /* Forward the request to the BlockDriver */ + /* Forward the request to the BlockDriver, possibly fragmenting it */ total_bytes = bdrv_getlength(bs); if (total_bytes < 0) { ret = total_bytes; @@ -1032,30 +1036,39 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs, } max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align); - if (bytes <= max_bytes) { + if (bytes <= max_bytes && bytes <= max_transfer) { ret = bdrv_driver_preadv(bs, offset, bytes, qiov, 0); - } else if (max_bytes > 0) { - QEMUIOVector local_qiov; - - qemu_iovec_init(&local_qiov, qiov->niov); - qemu_iovec_concat(&local_qiov, qiov, 0, max_bytes); - - ret = bdrv_driver_preadv(bs, offset, max_bytes, &local_qiov, 0); - - qemu_iovec_destroy(&local_qiov); - } else { - ret = 0; + goto out; } - /* Reading beyond end of file is supposed to produce zeroes */ - if (ret == 0 && total_bytes < offset + bytes) { - uint64_t zero_offset = MAX(0, total_bytes - offset); - uint64_t zero_bytes = offset + bytes - zero_offset; - qemu_iovec_memset(qiov, zero_offset, 0, zero_bytes); + while (bytes_remaining) { + int num; + + if (max_bytes) { + QEMUIOVector local_qiov; + + num = MIN(bytes_remaining, MIN(max_bytes, max_transfer)); + assert(num); + qemu_iovec_init(&local_qiov, qiov->niov); + qemu_iovec_concat(&local_qiov, qiov, bytes - bytes_remaining, num); + + ret = bdrv_driver_preadv(bs, offset + bytes - bytes_remaining, + num, &local_qiov, 0); + max_bytes -= num; + qemu_iovec_destroy(&local_qiov); + } else { + num = bytes_remaining; + ret = qemu_iovec_memset(qiov, bytes - bytes_remaining, 0, + bytes_remaining); + } + if (ret < 0) { + goto out; + } + bytes_remaining -= num; } out: - return ret; + return ret < 0 ? ret : 0; } /*